As an exhaust gas purifying system for purifying NOx in the exhaust gas of a diesel engine, an SCR system using an SCR (selective catalytic reduction) apparatus has been developed.
The SCR system supplies the urea aqueous solution upstream of the exhaust gas of the SCR apparatus, generates ammonia by heat of the exhaust gas, and reduces and purifies NOx on an SCR catalyst by the ammonia (see, for example, Patent Document 1).